SAO: Weekly Science Updates

Find out the latest thinking about our universe.
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SAO: Weekly Science Updates

Postby bystander » Sat Jul 12, 2014 8:55 pm

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SAO: Identifying Gamma Ray Blazars

Postby bystander » Sat Jul 12, 2014 10:02 pm

Identifying Gamma Ray Blazars
Smithsonian Astrophysical Observatory
Weekly Science Update | 2013 Oct 18

A blazar is a galaxy with an intensely bright central nucleus containing a supermassive black hole, much like a quasar. The difference is that a blazar can emit extremely high energy gamma rays -- light that is over a hundred million times more energetic than the highest energy X-rays as seen, for example, by the Chandra X-ray Observatory. Blazars are also generally characterized by having rapid and strong variability and a host of effects that result from its producing electrons moving close to the speed of light. Astronomers suspect that the bizarre behavior of blazars results when matter falling onto the vicinity of the massive black hole erupts into a powerful, narrow beam of high velocity charged particles. The intense X-ray, gamma ray, and infrared emission, and their variability as well, are thought to be the result of our fortuitously staring right down the throats of the jets. The orientation makes these objects unique probes of exotic physical activity. In most other galaxies, the infrared radiation comes from dust heated either by star formation or ultraviolet radiation from the vicinity of the massive black hole, rather than a blazar jet. ...

Identification of New Gamma-Ray Blazar Candidates With Multifrequency Archival Observations - Philip S. Cowperthwaite et al

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SAO: A Confirmed Distance Record for a Galaxy

Postby bystander » Sat Jul 12, 2014 10:26 pm

A Confirmed Distance Record for a Galaxy
Smithsonian Astrophysical Observatory
Weekly Science Update | 2013 Oct 25

About thirteen billion years ago the newborn universe began to produce stars. The first ones appeared only a few hundred million years after the big bang, but they were unlike stars of today. They were, for example, very massive because the infant universe consisted almost entirely of hydrogen and some helium and lacked the elements needed to form solar-type stars. By the time another half a billion years had passed, however, those stars and their descendants had manufactured enough other elements to enrich the natal gas and enable nearly normal stars to form. After a few billion years, galaxies themselves acquired their mature forms. Then, for reasons that are not well understood, galaxies began to make stars as much as ten times faster than they do today, until just a few billion years ago (also for poorly understood reasons) they settled back down into their current phase of activity. This general story has been known for a few decades but lately has become a more pressing research priority because our Milky Way participated in this history, and because the technology to answer such questions is now in hand. ...

A galaxy rapidly forming stars 700 million years after the Big Bang at redshift 7.51 - S. L. Finkelstein et al

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SAO: Tilted Suns

Postby bystander » Sun Jul 13, 2014 2:59 am

Tilted Suns
Smithsonian Astrophysical Observatory
Weekly Science Update | 2013 Nov 01

The Earth's axis of rotation is tilted 23.4 degrees to its orbital motion around the Sun (more precisely, its spin axis has a tilt of 23.4 degrees with respect to the axis of its orbit). This tilt, which causes our seasonal variations, was likely the result of a cataclysmic impact that occurred about 4.5 billion years ago between the Earth and another large body which probably also resulted in the formation of the moon. Such a large tilt is thought in general to result from a strong interaction between objects like the collision that formed the moon. Stars also spin, and their spin axes can also be tilted with respect to the orbits of their planets. In the case of our Sun, which spins roughly once every twenty-five days, its tilt is only 7.25 degrees, and so we never get a very good look at its north or south poles. Astronomers infer therefore that the Sun never had a traumatic encounter with another star (at least not since its planetary system formed, and at least not with a sudden collision). ...

A Giant Misalignment in a Multiple Planet System
NASA | Ames Research Center | Kepler | 2013 Oct 18

Stellar Spin-Orbit Misalignment in a Multiplanet System - Daniel Huber et al

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SAO: Old Young Stars

Postby bystander » Sun Jul 13, 2014 4:34 am

Old Young Stars
Smithsonian Astrophysical Observatory
Weekly Science Update | 2013 Nov 08

The early stages of a star's life are critical both for the star and for any future planets that might develop around it. The process of star formation, once thought to involve just the simple coalescence of material under the influence of gravity, actually entails a complex series of stages, with the youngest stars assembling circumstellar disks of material, possibly preplanetary in nature. In the current models, conservation of angular momentum during the collapse of cloud cores leads to the formation of these discs. The presence and evolution of these circumstellar discs is important both for the planets that form from them and for the star itself.

Stars start their lives by burning deuterium, an easier fuel to ignite than hydrogen (although it is less abundant). Stars that burn hydrogen are called main-sequence stars (the Sun is one), and they can continue in this stage of life for ten billion years or more depending on their mass (at least for stars of the Sun's mass or less). Stars young enough to still primarily burn deuterium are called pre main-sequence stars, and this stage of their life typically lasts a few hundreds of thousands of years or less (also depending sensitively on the initial mass of the star). The reason that circumstellar disks are so important for young stars (and not just for its planets) is because during the pre-main-sequence phase the star continues to grow in mass, and its growth comes from accreting gas from this disc. The time-scale of disc dissipation therefore sets crucial constraints for models of both star and planet development. ...

Pre-main sequence stars older than 8 Myr in the Eagle Nebula - Guido De Marchi et al
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SAO: Making the First Stars

Postby bystander » Sun Jul 13, 2014 4:26 pm

Making the First Stars
Smithsonian Astrophysical Observatory
Weekly Science Update | 2013 Nov 15
first_star-1.jpg

The first stars in the Universe are believed to have formed only a few hundred million years after the big bang, about 13.7 billion years ago. They heated and ionized the pristine intergalactic medium, and their supernova explosions enriched the primordial gas with the first heavy elements (the Universe was born with only hydrogen and a dash of helium). These stars thus altered in a fundamental way the chemical and thermal state of the gas from which the first galaxies then formed, in turn triggering the first self-sustaining cycle of star formation, feedback, and chemical enrichment. Understanding the formation and properties of the first stars is thus an important step towards a comprehensive picture of structure formation in the early Universe.

The first stars have yet to be directly observed. They are faint, although future space missions and giant telescopes hope to spot them. Meanwhile, theorists thinking about them have for several decades relied on basic physical concepts and computational simulations. In the current model, hydrogen and dark matter, coupled by gravity, form large structures at the centers of which molecular hydrogen gas forms. Molecular hydrogen can then radiate and cool the structures, allowing them to collapse further and heat up until stars are born. The final stages of the process occur rapidly and inside tiny volumes compared to the whole structure; both of these issues make it very difficult for the computations to track what's going on. As a result, there are major uncertainties, for example: how fragmentation at the final scale affects the birth weight of the stars produced. ...

On the Operation of the Chemothermal Instability in Primordial Star-Forming Clouds - Thomas H. Greif et al
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SAO: First Detection of Curled Ripples in Cosmic Background

Postby bystander » Sun Jul 13, 2014 4:43 pm

First Detection of Curled Ripples in the Cosmic Background
Smithsonian Astrophysical Observatory
Weekly Science Update | 2013 Nov 22

The universe was created 13.73 billion years ago in a blaze of light: the big bang. Roughly 380,000 years later, after matter (mostly hydrogen) had cooled enough for neutral atoms to form, light was able to traverse space freely. That light, the cosmic microwave background radiation, comes to us from every direction in the sky uniformly ... or so it first seemed. In the last decades, astronomers discovered that the radiation actually has very faint ripples and bumps in it at a level of brightness of only a part in one hundred thousand. These miniscule ripples reflect the architecture of the universe when the light was freed, and allowed the formation of the subsequent cosmic structures (galaxies and clusters of galaxies) as the light passed by them on its journey through space and time. The ripples hold clues, therefore, to the early universe and how it has evolved, and are consequently among the top priorities of modern astronomy research. ...

Detection of B-mode Polarization in the Cosmic Microwave Background with
Data from the South Pole Telescope
- D. Hanson et al (SPTpol Collaboration)

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SAO: First Confirmed Reverse Shock in a Gamma Ray Burst

Postby bystander » Sun Jul 13, 2014 5:04 pm

First Confirmed Reverse Shock in a Gamma Ray Burst
Smithsonian Astrophysical Observatory
Weekly Science Update | 2013 Nov 29

Gamma ray bursts (GRBs) are the brightest events in the known universe. These flashes of high-energy light occur about once a day, randomly, from around the sky. While a burst is underway, it is many millions of times brighter than an entire galaxy. Astronomers are anxious to decipher their nature not only because of their dramatic energetics, but also because their tremendous brightnesses enables them to be seen across cosmological distances and times, providing windows into the young universe.

The somewhat longer lasting variety of GRB is associated with the death of massive stars. The details of these bursts reflect the nature of the progenitor stars, the structure of the explosion environment, and the composition of the ejecta. Even after the explosion ends, the powerful ejecta generate an afterglow that can be analyzed as the particles plow into the circumstellar material around the progenitor star. Studies of the afterglow find two light signatures: one produced when a forward moving shock slams into the material, and a second kind resulting when a backward moving shock (the "reverse shock") is produced (roughly similar to the way a water wave, encountering an obstacle, spawns a backward moving wave). Both the forward and reverse shocks reveal different details of the cataclysm; the reverse shock is a particularly valuable probe of particle velocities in the burst. ...

A Reverse Shock in GRB 130427A - T. Laskar et al

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SAO: Probing A Local Starburst

Postby bystander » Sun Jul 13, 2014 5:41 pm

Probing A Local Starburst
Smithsonian Astrophysical Observatory
Weekly Science Update | 2013 Dec 06

Although many of the details about star formation are vigorously debated, the general principles are reasonably well understood. Stars form as the gas and dust in a molecular cloud coalesces until, under the influence of gravity, clumps develop dense enough to become stars. Occasionally a cluster of young stars can develop with many massive, hot, bright members (the Pleiades is an example of such a young cluster). On average, in a typical galaxy like our Milky Way a few stars are born every year. Astronomers have discovered, however, that there are ultra-luminous galaxies in the universe that are powered by starbursts in which hundreds of stars are forming per year in massive clusters. Some of these galaxies are even found during the cosmic dawn, when the universe was young. Astronomers wonder what prompts such such extreme cases, how the star formation processes might differ from normal ones to trigger such dramatic birthing, and if the stars produced in such bursts differ (statistically speaking) from those produced in normal star birth?

One difficulty in studying starbursts in other galaxies is that they are so far away the individual stars are indistinguishable. There are some massive starburst regions in our own galaxy that provide a nearer example. One of them, NGC6334, a giant molecular cloud with over one hundred million solar masses of gas and dust, is located only about two thousand light-years away. Its relative proximity gives scientists the ability to study such a starburst up close. CfA astronomers Sarah WIllis, Giovanni Fazio, and Howard Smith, together with three colleagues, have measured the stellar population using the infrared IRAC and MIPS cameras on the Spitzer Space Telescope, combined with a set of ground-based observations. ...

A Wide-Field Near- and Mid-Infrared Census of Young Stars in NGC 6334 - Sarah Willis et al

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SAO: Phosphorus in a Supernova Remnant

Postby bystander » Sun Jul 13, 2014 6:16 pm

Phosphorus in a Supernova Remnant
Smithsonian Astrophysical Observatory
Weekly Science Update | 2013 Dec 13

The element phosphorus is an indispensable ingredient for life along with carbon, oxygen, nitrogen, hydrogen, and sulfur. But phosphorus is much less abundant in the universe than these other elements -- in the solar system it is about three and one-half million times less common than hydrogen. Hence the mechanism(s) for making it are of particular interest to astronomers. All the elements except for hydrogen and some helium (which were made in the big bang) are the by-products of nuclear processing in stars. Scientists think that phosphorus is formed mainly in massive stars (more than about eight solar masses). These stars end their lives as supernova explosions, and current models conclude that most phosphorus is made either during a stage just prior to the explosion, or in layers during the explosion itself.

Freshly synthesized phosphorus should be present in the remnants of supernovae from massive stars if these theories are correct. CfA astronomer John Raymond and his colleagues studied the phosphorus in the remnant Cassiopeia A, which lies about eleven light-years away and was made in an explosive event in the year 1681. The team examined the near-infrared emission line of phosphorus at multiple locations around the remnant, and used its strength compared to other species, as well as the motions of the gas, to describe the processes responsible. The astronomers are able to confirm the models and, at least least in the case of this supernova remnant, refine the details of the key mechanisms responsible.

Phosphorus in the Young Supernova Remnant Cassiopeia A - Bon-Chul Koo et al
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SAO: Retrieving an Asteroid

Postby bystander » Sun Jul 13, 2014 6:50 pm

Retrieving an Asteroid
Smithsonian Astrophysical Observatory
Weekly Science Update | 2013 Dec 20

Asteroids (or comets) whose orbits bring them close to the earth's orbit are called near Earth objects. Some of them are old, dating from the origins of the solar system about four and one-half billion years ago, and expected to be rich in primitive materials. They are of great interest to scientists studying the young solar system. Others, of lower scientific priority, are thought to contain minerals of potential economic value.

NASA has announced its interest in sending a manned mission to a near Earth object. The NASA Asteroid Robotic Retrieval Mission concept involves the capture of an asteroid, and dragging it onto a new trajectory that traps it in the Earth–Moon system where it will be further investigated by astronauts. The current mission design requires the target asteroid to have a diameter of seven to ten meters. The object NEO 2009BD is a prime candidate for this retrieval mission. It was discovered on January 16, 2009, at a distance from the Earth of only 0.008 AU (one AU is the average distance of the Earth from the Sun). Its orbit is very Earth–like, with a period of 400 days, and it will end up close to the Earth–Moon system again in late 2022 when the proposed capture would take place. It seems to be a perfect candidate, with a time frame that allows for proper mission planning.

The problem is that the size of the NEO 2009BD is uncertain, and thus its density and composition are also uncertain, but first estimates are that it likely falls in the diameter range specified by the mission. The uncertainty arises because it was detected at optical wavelengths; they measure reflected light, which is a combination of both an object's size and reflectivity (albedo). For NASA mission planning to succeed, a more direct size measurement of 2009 BD is needed -- and soon, before its increasing distance from the Earth makes such an observation a practical impossibility. ...

Constraining the Physical Properties of Near-Earth Object 2009 BD - M. Mommert et al

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SAO: A New Look at Star Formation in Molecular Clouds

Postby bystander » Sun Jul 13, 2014 7:22 pm

A New Look at Star Formation in Molecular Clouds
Smithsonian Astrophysical Observatory
Weekly Science Update | 2013 Dec 27

Our Milky Way, like other galaxies, assembled over cosmic time from rarefied, gaseous material into immense, regular systems of hydrogen-burning stars. The processes responsible for this star formation were complex and operated over most of cosmic history - and they are not yet fully understood. A predictive theory of star formation is essential to an understanding galaxy formation and evolution, and an important step in that direction is discerning an empirical relation that connects the rate of star formation to the physical properties of the interstellar gas. For over half a century, astronomers have thought that the rate of star formation depends on the gas density, such that the number of stars formed per year varies roughly as gas density to some power, with the scaling usually taken to be approximately as the density squared.

The original conjecture relating star formation to gas density was made for galaxies as a whole. CfA astronomers Charlie Lada and Jan Frobrich and their colleagues examined star formation in four giant molecular clouds in our galaxy to test the extent to which this behavior accurately characterizes physical processes within individual clouds. They were motivated in part by the curious fact that on the one hand star formation rates (numbers of stars per year) do seem to follow this kind of scaling law, yet on the other hand the total numbers of new stars present do not seem to correlate with gas density. The scientists used infrared data from the Spitzer Space Telescope and ground-based, near infrared surveys to perform statistical analyses, comparing star formation over small spatial scales against the gas and dust density as tracked by the amounts of visual obscuration. ...

Schmidt's Conjecture and Star Formation in Molecular Clouds - Charles Lada et al

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Re: SAO: Weekly Science Updates

Postby MargaritaMc » Sun Jul 13, 2014 8:05 pm

Great work, bystander! It is SO HELPFUL to have them linked with any related arXiv papers, as you've done. Thank you very much!

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SAO: A Superluminous Supernova

Postby bystander » Sun Jul 13, 2014 10:21 pm

A Superluminous Supernova
Smithsonian Astrophysical Observatory
Weekly Science Update | 2014 Jan 03

Supernovae are the explosive deaths of massive stars. Among the most momentous events in the cosmos, they disburse into space all of the chemical elements that were produced inside their progenitor stars, including most of the elements essential for making planets and life. Astronomers have recognized for decades that there are several different kinds of supernovae, most fundamentally those that originate from a single massive star and those that develop when one member of a pair of binary stars becomes massive by feeding on its neighbor. Other factors like the stellar composition also come into account. Sorting out all these various complications is critical if astronomers want to be able to reliably classify any particular supernovae and thereby infer its intrinsic brightness, and then use its observed brightness as a measure of its distance.

Recent wide-field surveys searching for supernovae have found that the conventional schema for classifying supernovae may be even more complicated than previously thought. A few years ago a new class called superluminous supernovae was found, characterized by their emitting total radiated energies equal to about ten billion suns shining for a year. Some of these new objects were discovered at cosmological distances, helping to cement the notion that new types were being discovered, and further studies have found even more subdivisions, also based among other things on composition. These new superluminous supernovae can be identified and characterized by the particular way their light fades away after the brightness peak, driven in part by the radioactive decay of elements manufactured in the explosions. ...

The Superluminous Supernova PS1-11ap: Bridging the Gap between Low and High Redshift - M. McCrum et al
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SAO: Clouds in the Atmosphere of a Super-Earth Exoplanet

Postby bystander » Sun Jul 13, 2014 10:49 pm

Clouds in the Atmosphere of a Super-Earth Exoplanet
Smithsonian Astrophysical Observatory
Weekly Science Update | 2014 Jan 10

As of the start of the new year, 2014, there were about 1056 confirmed planets around stars other than our Sun ("exoplanets"), including 175 multiple planet systems. Surveys have found that planets intermediate in size between Earth and Neptune, the so-called "super-Earths," are among the most common planets in the galaxy (about 140 are known). Modeling the atmospheres of these objects is the next step towards developing a comprehensive understanding of the class, and astronomers are working to obtain spectra of the atmospheres to characterize them.

There are three basic spectroscopic techniques used to study an exoplanet's atmosphere: transmission (the star's light is transmitted or absorbed as it passes through the planet's atmosphere), emission (light is emitted directly by the atmospheric gases), or reflection (the atmospheric clouds or gases selectively reflect the star's light). Transmission spectroscopy is particularly apt for transiting exoplanets because they pass in front of the star, and there have been numerous attempts to use it in the case of the transiting super-Earth archetype GJ 1214b. Astronomers suspected that its atmosphere was either dominated by relatively heavy molecules like water, or that it contained high-altitude clouds that obscured its lower layers, but the observations so far have not had enough precision to distinguish between these options. ...

Blue Light Observations Indicate Water-Rich Atmosphere of a Super-Earth
Subaru Telescope | National Astronomical Observatory of Japan | 2013 Sep 03

Hubble Sees Cloudy Super-Worlds with Chance for More Clouds
NASA | STScI | HubbleSite | 2013 Dec 31

Clouds in the Atmosphere of the Super-Earth Exoplanet GJ 1214b - Laura Kreidberg et al

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SAO: Pluto and its Moons

Postby bystander » Mon Jul 14, 2014 1:01 am

Pluto and its Moons
Smithsonian Astrophysical Observatory
Weekly Science Update | 2014 Jan 17

In 1978, the dwarf planet Pluto was discovered to have a companion, called Charon. With a mass about 12% Pluto’s mass, Charon orbits its partner about seventeen Pluto-radii away (for comparison, our Moon has less than 2% of the Earth's mass and orbits about sixty Earth-radii away). But that’s not all. By 2012 astronomers had added four other satellites to the Pluto family: Styx, Nix, Kerberos, and Hydra. Their masses are still very uncertain, but the combined mass is estimated to be a few millionths of the mass of Pluto.

Astronomers wonder where these small satellites came from, how they acquired their stable configuration without first wandering off as their gravity perturbed one another, and how the answers to these questions can help clarify the formation and evolution processes of planetary systems in general. Current theories argue that the system formed from a giant impact between two icy objects with a total mass about 30% larger than Pluto’s current mass. Immediately after the event Charon was much closer to Pluto, but then it drifted away over a period of about one to ten million years. Some versions of the model predict that the other four siblings also formed during the initial impact, and also moved away, but with so many bodies in the family that is not so easy to do yet hold together in the regular pattern observed. A competing theory argues that the Pluto-Charon pair, after the impact, had a circumbinary disk of small objects that gradually coalesced into the four sibling moons. ...

Pluto satellites’ orbital ballet may hint of long-ago collisions
Southwest Research Institute | 2013 Oct 09

The Formation of Pluto's Low Mass Satellites - Scott J. Kenyon, Benjamin C. Bromley
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SAO: Fast and Furious: Shock Heated Gas in Colliding Galaxie

Postby bystander » Mon Jul 14, 2014 1:26 am

Fast and Furious: Shock Heated Gas in Colliding Galaxies
Smithsonian Astrophysical Observatory
Weekly Science Update | 2014 Jan 24

Luminous infrared galaxies shine with the radiative output of tens of Milky Way galaxies, or even more. Their most striking feature, however, is not their tremendous energy output but the fact that nearly all of their radiation is invisible and at infrared wavelengths. The source of the energy is intense star formation that takes place within dust-filled clouds. The ultraviolet and visible light produced by hot young stars is absorbed by the dust grains and is then remitted as infrared radiation. Collisions between galaxies are expected to trigger enhanced star formation, and so luminous galaxies are thought to result from such interactions. These objects may be representative of a phase of stellar growth and enrichment that most galaxies briefly experience, especially during early times in the age of the universe when collisions were more common. The connections between galaxy interactions and star formation, however, are imperfectly understood, in part because the obscuring dust makes it difficult to probe the small nuclei of merging galaxies.

In the local universe (that is, within a billion light-years or so of us) the galaxy NGC6240 is unusual, being a luminous infrared source in the throes of a major merger of two galaxies, experiencing star formation at an estimated rate of about twenty-five solar masses per year, and radiating about twenty times as much energy as does the Milky Way. It is also known to be a powerful emitter of X-rays. The origin of these X-rays has been uncertain: they could., for example, come from intermediate-sized black holes formed in the star formation process, or perhaps from the supermassive black holes at the center of the nuclei. ...

NGC 6240: Colossal Hot Cloud Envelops Colliding Galaxies
NASA | MSFC | SAO | CXC | 2013 Apr 30

Fast and Furious: Shock Heated Gas as the Origin of Spatially Resolved
Hard X-ray Emission in the Central 5 kpc of the Galaxy Merger NGC 6240
- Junfeng Wang et al
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SAO: X-Ray Emission from Star-Forming Galaxies

Postby bystander » Mon Jul 14, 2014 2:25 am

X-Ray Emission from Star-Forming Galaxies
Smithsonian Astrophysical Observatory
Weekly Science Update | 2014 Jan 31

Star formation lights up a galaxy because many newly formed stars are massive, hot and bright. These young stars are made in dusty clouds of material that obscure their visible light, and so luminous galaxies in our universe are often optically dim. But the dust absorbs the light and re-radiates it at infrared wavelengths, and astronomers can use the infrared from galaxies to infer the rate of star formation activity underway, even without seeing those stars. The method does not always work well, however: other processes can heat up dust and lead to an overestimate of the star formation rate, for example an active black hole at the nucleus; on the other hand sometimes the dust does not effectively absorb all of the light, leading to an underestimate of the rate.

There are three dominant sources of X-ray emission in galaxies: very hot interstellar gas, massive compact binary stars that emit X-rays (both of these a result of star formation), and accretion that heats material around a black hole nucleus. Astronomers would like to use X-ray emission as an alternate measure of star birth activity because of the issues arising with infrared dust emission, but the problem is addressing contamination from nuclear emission. ...

X-ray Emission from Star-Forming Galaxies – III. Calibration of the LX−SFR Relation Up to Redshift z ≈ 1.3 - S. Mineo et al
X-ray Emission from Star-Forming Galaxies – II. Hot Interstellar Medium - S. Mineo et al
X-ray Emission from Star-Forming Galaxies – I. High-Mass X-ray Binaries - S. Mineo et al
X-ray Emission from Star-Forming Galaxies – Signatures of Cosmic Rays and Magnetic Fields - Jennifer Schober et al
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SAO: Watching Gas Clouds Move

Postby bystander » Mon Jul 14, 2014 6:34 pm

Watching Gas Clouds Move
Smithsonian Astrophysical Observatory
Weekly Science Update | 2014 Feb 07

A maser, like a laser, is a source of bright electromagnetic radiation, with the difference being that maser radiation is not optical light but rather longer wavelength, microwave radiation. Small, dense molecular clouds in interstellar space sometimes produce natural masers; water vapor in clouds undergoing active star formation generates some of the most spectacular such masers. In the most dramatic cases, a water vapor maser can radiate more energy at a single wavelength than does the Sun over its entire visible spectrum.

Masers are interesting in their own right, but also because their bright emission provides a powerful diagnostic probe of regions where massive star formation is still underway. CfA astronomer Nimesh Patel and his colleagues have used a coordinated set of widely separated radio telescopes (an interferometer) to study a dramatic region of star formation about ten thousand light-years away, achieving a spatial resolution of only a few hundred astronomical units (one AU is the average distance of the Earth from the Sun). This spectacular precision is possible because the masers are so bright. ...

Multi-epoch VLBA H2O maser observations toward the massive YSOs AFGL 2591, VLA 2 and VLA 3 - J. M. Torrelles et al
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SAO: Do Black Holes Have Hair?

Postby bystander » Mon Jul 14, 2014 7:30 pm

Do Black Holes Have Hair?
Smithsonian Astrophysical Observatory
Weekly Science Update | 2014 Feb 14

Black holes with masses of millions or even billions of suns appear to reside at the nuclei of galaxies. In dramatic cases like quasars they are thought to be responsible for the spectacular phenomena like the ejection of narrow jets of particles at nearly the speed of light. Such outflows are thought to be driven by matter accreting onto a hot disk around the black hole. Much smaller black holes, closer in size to one solar mass, are thought to form as the result of the cataclysmic death of a star in a supernova.

A black hole in the traditional theory is characterized by having “no hair”; that is, it is so simple that it can be completely described by just three parameters, its mass, its spin, and its electric charge. Even though it may have formed out of a complex mix of matter and energy, all the specific details are lost when it collapses to a singular point. In the standard paradigm, the black hole is surrounded by a “horizon,” and once anything – matter or light (energy) – falls within that horizon, it cannot escape. Hence, the singularity appears black. Outside this horizon an accreting disk (if there is one) can radiate freely. ...

Distinguishing Black Holes from Naked Singularities Through Their Accretion Disc Properties - Pankaj S. Joshi, Daniele Malafarina, Ramesh Narayan

SISSA: Do Black Holes Have 'Hair'?

Black holes with surrounding matter in scalar-tensor theories - Vitor Cardoso et al

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SAO: The Evolution of Galaxies that Host Massive Black Holes

Postby bystander » Tue Jul 15, 2014 4:01 am

The Evolution of Galaxies that Host Massive Black Holes
Smithsonian Astrophysical Observatory
Weekly Science Update | 2014 Feb 21

Our Milky Way galaxy, like most galaxies, has a nucleus with a massive black hole. Our nuclear black hole contains about four million solar masses of material, but others are thought to have hundreds of millions of solar masses or even more. Around the core, according to theories, is a torus of dust and gas whose inner edge can be heated to millions of degrees by material falling into the black hole, a process called accretion. Accretion heating can sometimes drive bipolar jets of rapidly moving charged particles, which radiate at radio wavelengths and are detected as bright cosmic radio sources.

Galaxies frequently collide, and it has been predicted that such mergers tend to push material towards the central black holes, thus fueling the accretion process. There is a variety of evidence in favor of this scenario, including the fact that more massive black holes are found in more massive galaxies, possibly the results of mergers. However, there is some conflicting evidence. By some accounts there are not enough merging galaxies to account for all the massive black holes that are seen. Moreover, galaxies and their black holes can also grow and evolve by more mundane processes such as normal gas inflow to the cores. Finally, most galaxies from an epoch a few billion years ago appear to be relatively normal objects, and not undergoing collisions. ...

Tracing the Evolution of Active Galactic Nuclei Host Galaxies Over the Last 9 Gyr of Cosmic Time - Andy D. Goulding et al
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SAO: An Extended Gamma-Ray Source with No Known Counterpart

Postby bystander » Tue Jul 15, 2014 4:35 am

An Extended Gamma-Ray Source with No Known Counterpart
Smithsonian Astrophysical Observatory
Weekly Science Update | 2014 Feb 28

Gamma-rays are the most energetic known form of electromagnetic radiation, with each gamma ray being at least one hundred thousand times more energetic than an optical light photon. The most potent gamma rays, the so-called VHE (very high energy) gamma rays, pack energies a billion times this amount, or even more. Astronomers think that VHE gamma rays are produced in the environment of the winds or jets of the compact, ultra-dense remnant ashes of massive stars left behind from supernova explosions.

There are two kinds of compact objects produced in supernovae: black holes and neutron stars (stars made up predominantly of neutrons, having densities equivalent to the mass of the Sun packed into a volume about 10 kilometers in radius). The winds or jets from the environments of such objects, including the kind called pulsars, can accelerate charged particles to very close to the speed of light. When light scatters off such energetic particles it becomes energized as well, sometimes turning into VHE gamma rays. At least this is the most popular current theory. One of the first known VHE sources was spotted about fifteen years ago in the direction of the constellation of Cygnus. It was unusual because, unlike most other known VHE sources which had counterparts seen at optical, radio, or other wavelengths, this new source had no known counterpart. With no other information available, its exact nature was mysterious. ...

Observations of the Unidentified Gamma-Ray Source TeV J2032+4130 BY VERITAS - VERITAS Collaboration: E. Aliu et al
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SAO: Star Formation in Luminous, Colliding Galaxies

Postby bystander » Wed Jul 16, 2014 4:55 pm

Star Formation in Luminous, Colliding Galaxies
Smithsonian Astrophysical Observatory
Weekly Science Update | 2014 Mar 07

Nearly thirty years ago the Infrared Astronomy Satellite discovered that the universe contained many tremendously luminous galaxies, some more than a thousand times brighter than our own Milky Way, but which are practically invisible at optical wavelengths. They are powered by bursts of star formation buried deep within clouds of dust and gas; the dust absorbs the optical light while radiating at infrared wavelengths.

Astronomers suspect that in many cases the hyperactivity was triggered by a collisional encounter that facilitated the collapse of interstellar gas into new stars. Collisions between galaxies are common. Indeed, most galaxies have probably been involved in one or more encounters during their lifetimes, making these interactions an important phase in galaxy evolution and the formation of stars in the universe. The Milky Way, for example, is bound by gravity to the Andromeda galaxy and is approaching it at a speed of about 50 kilometers per second; we are expected to meet in another billion years or so. In the local universe, such encounters can be easily identified by the visible morphological distortions they produce such as tidal tails sweeping out from the galactic discs. But not all infrared luminous galaxies show such distortions; moreover, luminous galaxies in the more distant cosmos are too remote to detect these spatial signatures (at least with current telescopes). Astronomers are therefore working to understand when and how collisions stimulate star formation, whether that star formation resembles conventional star formation or differs (perhaps by making more massive stars, for example), and to determine if some alternative to visual morphology can also quantify these effects. ...

Simulated Galaxy Interactions as Probes of Merger Spectral Energy Distributions - Lauranne Lanz et al
The Total Infrared Luminosity May Significantly Overestimate
the Star Formation Rate of Recently Quenched Galaxies
- Christopher C. Hayward et al
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SAO: The Workings of an X-ray Binary Star

Postby bystander » Wed Jul 16, 2014 5:36 pm

The Workings of an X-ray Binary Star
Smithsonian Astrophysical Observatory
Weekly Science Update | 2014 Mar 14

The bright X-ray source known as LMC X-3 resides in the Large Magellanic Cloud, the dwarf galaxy that is the Milky Way’s nearest neighbor. Two decades ago astronomers discovered that the source is actually a binary system with a normal star rapidly orbiting a nearby black hole (whose mass is about 2.3 solar-masses) in only 1.7 days. In X-ray binary systems like this one, material from the normal star falls onto a disk around the black hole, causing it to glow and emit radiation – at X-ray wavelengths from the inner portion of the disk closest to the black hole, and at infrared wavelengths from the outer portions of the disk. The emission typically varies in time, presumably because the infalling matter arrives in clumps or in an uneven stream. The infrared and X-ray emissions also vary from one another, and astronomers have long thought that modeling their behaviors might lead to an enhanced understanding of black hole accretion processes. ...

Modeling the Optical–X-ray Accretion Lag in LMC X-3: Insights into Black-Hole Accretion Physics - James F. Steiner et al
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SAO: Transition Disks Around Young Stars

Postby bystander » Wed Jul 16, 2014 6:17 pm

Transition Disks Around Young Stars
Smithsonian Astrophysical Observatory
Weekly Science Update | 2014 Mar 21

A star is typically born with a disk of gas and dust encircling it, the spinning remnant of the much larger cloud of natal material. As the star begins to shine, planets develop from the dust grains in the disk as they stick together and grow. Although the vast majority of very young stars show indirect evidence for such circumstellar disks, in only a few cases have disks been imaged directly or studied in any detail because their sizes on the sky are small (much smaller than the atmospherically blurred sizes of the stars themselves), and in most situations they are fainter than their parent stars. The discovery of ubiquitous planets (“exoplanets”) around other stars lends further credence to the ideas about disks, and adds to the need for an improved understanding of the details of disk formation, structure, and evolution.

Young disks are known to emit at infrared wavelengths because they are warmed by the star to temperatures above the cold, ambient interstellar dust. Astronomers use the particular colors of the star and disk system to characterize the young disk’s properties. After about five million years, however, nearly all stars lack evidence of warm circumstellar dust, suggesting that most disks (or at least around stars roughly the size of the Sun) have disappeared by this time: the disk material has been accreted onto the star or converted into planets or sub-planet-sized bodies, or else dispersed via ultraviolet evaporation or winds. So-called transition disks bridge the gap between the end points of disk evolution: They have not yet been disbursed, but although they are present they emit only slightly in the infrared, at characteristically cooler temperatures. ...

High-Resolution Submillimeter and Near-Infrared Studies of the Transition Disk Around Sz 91 - Takashi Tsukagoshi et al
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